There is provided a child car seat capable of preventing a seat body from being unintentionally moved to a turning position. A pedicle screw cluster derotation tool simultaneously engages multiple pedicle screws and transmits rotative forces to multiple vertebrae to effect a whole-spine correction. A projection integrated with the auxiliary magnetic pole layer is formed in a recess of the nonmagnetic material layer on the groove. The specific digital value is associated with the particular memory address received from the host.